An automatic transmission may include a torque converter for transmitting power of an engine, a planetary gear set for receiving power from the torque converter, shifting power according to a vehicle speed and transferring the shifted power to an output shaft, and a plurality of clutches and a brake installed to change a speed by controlling the planetary gear set.
The automatic transmission may have a hydraulic system supplying oil to lubricate a lubrication element (a bearing, a bush, or a gear), cool a cooling element (an electric motor, etc.), and form a control pressure of a control element (a clutch, a brake, or a torque converter).
The hydraulic system of the automatic transmission may have a valve body in which a plurality of hydraulic passages and a plurality of valves are prepared and an oil pump for supplying oil to the hydraulic passages of the valve body.
FIG. 1 is a view illustrating a partial structure of a valve body 10.
Referring to FIG. 1, an oil pan 21 for storing oil may be disposed below the valve body 10, and an oil pump 22 may be connected to the oil pan 21. A plurality of hydraulic passages such as a first hydraulic passage 11 and a second hydraulic passage 12 may be formed in the valve body 10. A regulator valve 13 may be disposed between the first hydraulic passage 11 and the second hydraulic passage 12, and a torque converter control valve 14 controlling a torque converter 15 may be installed in the middle of the second hydraulic passage 12. A first re-circulation passage 31 may extend from the regulator valve 13 to the oil pan 21, and a second re-circulation passage 32 may extend from the torque converter control valve 14 to the oil pan 21. The first re-circulation passage 31 and the second re-circulation passage 32 may join at one point and connect to the oil pan 21.
As oil is pumped by the oil pump 22 from the oil pan 21 and supplied to the regulator valve 13 through the first hydraulic passage 11, line pressure may be formed in the first hydraulic passage 11.
The regulator valve 13 may convert the line pressure supplied through the first hydraulic passage 11 into control pressure and output the control pressure, and the control pressure may be supplied to the torque converter control valve 14, appropriately converted by the torque converter control valve 14, and may be supplied to a control element such as the torque converter 15.
The valve body 10 may be installed on one side of a housing of the automatic transmission, and thus, when the vehicle is parked for a long period of time, oil within the valve body 10 may move downwardly due to gravitation to cause an empty space without oil to be formed in the hydraulic passages. Accordingly, the first re-circulation passage 31 and the second re-circulation passage 32 of the valve body 10 may become filled with air. In this state, when the vehicle, which has been parked for a long period of time, is initially started, air of the re-circulation passages 31 and 32 may be drawn into to the oil pump 22 to cause noise (which may be an abnormal noise).
In detail, in a case in which when pressure in the first hydraulic passage 11 is high, high pressure may instantly pushes air to the re-circulation passages 31 and 32, and thus, air within the re-circulation passages 31 and 32 is rapidly reduced in volume at a discharge port of the oil pump 22, generating noise (which may be an abnormal noise).
Also, after the initial starting, the re-circulation passages 31 and 32 may be filled with oil, and thus, a noise may not be not generated when the vehicle is started for the second time and thereafter.
In this manner, in past procedures of the related art, when the vehicle is initially started after having been left parked for a long period of time, noise may be made due to high line pressure within the valve body of the automatic transmission and such noise may cause an adverse reaction and make a driver feel uneasy.